1. Field of Art
The present invention relates to high pressure fluid pumps wherein the pump essentially includes a motor-driven piston for producing high pressure fluid outputs. The present invention more particularly relates to a high pressure fluid pump used in a gas-liquid relative permeameter incorporating a low horse power motor to provide additive motive power and incorporating a stress intensifier in the form of a booster piston to provide the majority motive power.
2. Discussion of Prior Art Results
Conventional gas-liquid relative permeameters in the analysis of oil field core samples require low-pressure delivery of gas in the range of a few psig to several hundred psig. There is a need to deliver high pressure gas to such core samples in order to more closely simulate the high underground pressures that occur in reservoirs from which the samples are taken. To deliver such high pressures, a large horse power
such in the range of 0.75 Hp to 2 Hp is required to drive a pump wherein the piston in the pump displaces the gas from a chamber between the piston and the cylinder of the pump at rates of 25 to 500 cm.sup.3 /min at the desired level of high pressure in a range of 500 to 7,000 psig. Such large horse power motors are expensive, occupy a large amount of space and generate environmental heat and noise. In addition, the high torque required to drive the piston causes significant wear to the costly ball screw interconnecting the piston with the motor. As a result, such high pressure permeameters are not conventionally available.
Therefore, this invention provides a new range of low power gas-liquid permeameters that simulates the high pressure reservoir conditions. Such "new-range" gas-liquid relative permeameters require the delivery and recirculation of high pressure gases and liquids. Although the delivery pressure is high, the differential pressure across a reservoir rock sample being tested (a core plug) is normally quite small. To illustrate: under the teachings of the present invention, gas and/or liquids may be delivered to a core plug at a pressure of 7000 psig. However, the pressure loss suffered by these fluids as they pass through the core plug may only be 50 psi; hence, they exit the sample at a pressure of 6950 psig. Suppose that the fluid being circulated is a gas. In a gas recirculating system with a conventional pump, the energy from the high pressure exit gas is wasted; i.e., even though it tends to cause the piston in the receiving pump to be pushed back (retreated), this force is resisted by an electric motor attached to the receiving pump. In the embodiment of the present invention, however, some of the energy of the exiting gas is captured, and is used to help drive the advancing piston in the delivery pump. The electric motors in the pumps of the present invention are required to supply energy only to overcome the aforesaid differential pressures plus the friction in the pumps. Because only the relatively small differential pressure is involved, instead of the total system pressure, the power output required of the motors is considerably reduced.
Prior to the filing of the present application, a search was conducted. The results of the search are:
______________________________________ Inventor U.S. Pat. No. Issued ______________________________________ Raymond 1,513,422 10-28-24 Prellwitz 1,636,614 7-19-27 Brink 2,724,963 11-29-55 Glasgow 3,070,023 12-25-62 Moore 3,502,001 3-24-70 Turner et al. 4,083,228 4-11-78 Pauliukonis 4,457,210 7-3-84 ______________________________________
The 1978 patent to Turner (U.S. Pat. No. 4,083,228) relates to a gas comparison pycnometer for accurately determining the volume of a condensed material sample. Turner utilizes two substantially equal but variable volume gas containing chambers--one as a sample chamber and one as a reference chamber. In the sample chamber is placed a volume compensation piston driven by a micrometer. The volume compensation piston is adjusted into the sample chamber by a micrometer thereby increasing the volume of the sample receiving chamber in order to maintain the equal free space volume between the sample chamber and the reference chamber. This provides a highly accurate determination of the sample volume.
The 1955 patent to Brink (U.S. Pat. No. 2,724,963) sets forth a positive displacement mercury volumetric pump driven by an adjustable-constant speed drive to permit continual displacement of mercury at a selectable flow rate, into a core holder holding a core sample from a sub-surface oil bearing reservoir.
The 1984 patent to Pauliukonis (U.S. Letters Pat. No. 4,457,210) discloses an energy conserving air motor capable of converting linear motion into rotary motion. To accomplish this, Pauliukonis utilizes a unitary piston design having a large diameter end and a small diameter end with a pathway through the center of the piston for delivering the air to the opposing pistons. Air is delivered behind the smaller diameter piston to drive the piston and to generate rotary work output. When fully driven, the air is delivered through the pathway in the center of the piston to penetrate behind the larger diameter piston thereby causing the larger diameter piston to return the piston to the working position.
The 1970 patent to Moore (U.S. Pat. No. 3,502,001) sets forth a fluid operated cylinder which is adapted to sense whether or not a load requires work. In the event that a load requires work, the valve within the piston is closed and the cylinder operates to engage the work piece and provide a work stroke. In the event that no load is present, the valve remains open and the working fluid is delivered from one side of the piston to the other side.
The 1962 patent to Glasgow (U.S. Pat. No. 3,070,023) relates to a fluid operated pump capable of pumping fluids under relatively high pressures utilizing a low or intermediately pressurized fluid as the source of motive power. Hence, a low pressure motive fluid is delivered to a larger diameter piston to drive he lower diameter piston thereby pumping the working fluid at a magnitude of several thousands pounds per square inch.
The 1924 patent to Raymond (U.S. Pat. No. 1,513,422) is essentially an air compressor for providing higher and lower air pressure outputs based upon utilizing two interconnected pistons of different diameters. The larger diameter piston provides the standard compression for air whereas the second piston of smaller diameter provides the higher pressures.
The 1927 patent to Prellwitz (U.S. Pat. No. 1,636,614) like Raymond, provides a multi-stage compressor for providing a variety of pressure ranges based upon differing sized pistons.
None of the above references disclose the features of the hybrid high pressure fluid pump of the present invention which is particularly adapted for gas-liquid relative permeability tests.